CN107025359A - The calculating of the knife work interface cutting behavior otherness of left and right cutting edge and method of testing - Google Patents

Abstract

Calculation and test method of cutting behavior difference between left and right cutting edge at tool interface. In order to solve the problem that the existing test methods do not have a test method that can fully reveal the difference in cutting behavior of cutting tools for cutting large-pitch trapezoidal external threads. The invention includes: determining the hierarchical structure and characteristic variables of the tool contact relationship in turning large-pitch threads; calculating and analyzing the tool contact length and tool contact width of the left and right blades; establishing the force model of the left and right cutting tools; using the left and right cutting edges of the tool The calculation method of deformation coefficient and relative slip, the calculation method of shear angle and friction angle, and the experimental test method of cutting behavior difference reveal the shape of chips when cutting left and right edges, the wear of left and right edges and the dynamic cutting behavior of left and right edges. difference. The invention discloses the differences in chip shape, wear of the left and right blades, and dynamic cutting behavior of the left and right blades when the left and right blades are cutting, and provides an effective basis for improving the quality of the processed surface.

Description

Calculation and test method of cutting behavior difference between left and right cutting edge

technical field

The invention relates to a method for testing the difference in cutting behavior of a tool for cutting large-pitch trapezoidal external thread, in particular to a method for calculating and testing the difference in cutting behavior of the left and right cutting edges of the tool for turning large-pitch trapezoidal external thread.

Background technique

As the main component of the press to control the parallelism and perpendicularity of the upper and lower dies, the large-pitch screw has an important impact on the static and dynamic accuracy of the whole machine. During processing, the processing accuracy of the left and right thread surfaces requires high consistency. When turning large-pitch threads, the cutting behavior of the left and right blade tool interfaces is different, which directly affects the surface quality of the left and right thread surfaces and the consistency of the surface quality of the left and right thread surfaces. Therefore, it is of great significance to study the difference in cutting behavior of the left and right cutting edges on the tool interface to improve the surface quality of the left and right thread surfaces and the consistency of the surface quality of the left and right thread surfaces.

Existing studies use the trilinear interpolation method to determine the points in the contact area according to the distance value, and obtain the relevant parameters of the tool contact relationship from these points, and analyze the characteristics of the tool contact geometry during the machining process. At the same time, research has been conducted to detect the change characteristics of the tool contact through the characteristic change of the power spectrum of the spindle vibration signal. However, the above method does not consider the changes in chip shape and tool wear during machining, and cannot fully reveal the cutting behavior of the tool interface, and the difference in cutting behavior of the tool interface between the left and right cutting edges during large-pitch thread turning has not been revealed.

Contents of the invention

The purpose of the present invention is to solve the problem that the existing test methods do not have a test method that can fully reveal the difference in cutting behavior of cutting tools for cutting large-pitch trapezoidal external threads, and then provide calculation and testing for the difference in cutting behavior of the left and right cutting edges. method.

The technical solution of the present invention is: the technical solution adopted for realizing the above object is to comprise the following steps:

The first step is to determine the hierarchical structure and characteristic variables of the tool-worker contact relationship in turning large-pitch threads;

According to the cutting motion and posture of the tool during the cutting process, the characteristic parameters and influences of the contact behavior of the tool interface are identified.

Influencing factors, analyzing the hierarchical structure and characteristic variables of the knife-worker contact relationship;

The second step is the calculation and analysis of the contact length and width of the left and right blades;

The third step is to establish the force model of the left and right cutting tools;

The fourth step is to use the deformation coefficient and relative slip calculation method of the left and right cutting edges of the tool to reveal the difference in cutting deformation between the left and right cutting edges of the tool;

The fifth step is to use the shear angle and friction angle calculation method of the left and right cutting edges of the tool to reveal the difference in the friction process of the left and right cutting edges of the tool;

The sixth step is to use the experimental test method of the difference in the cutting behavior of the left and right cutting edges of the tool to reveal the differences in the chip shape, wear of the left and right edges, and the dynamic cutting behavior of the left and right edges when cutting the left and right edges;

In order to adopt a forming turning tool with symmetrical left and right blades, under the same process parameters, the left and right thread surfaces of the threaded specimens are dry-turned with equal margins. Chip shape and through the DH5922 transient signal test and analysis system to test the time domain and frequency domain vibration signals of the tool when the left and right blades turn large-pitch threads for the last cut, and analyze the test results of the difference in cutting behavior between the left and right blades of the tool.

Furthermore, the formula for the initial contact length between the tool flank and the machined surface in the second step is:

(1) The formula for the initial contact length between the left flank of the tool and the machined surface is:

(2) The formula for the initial contact length between the right flank of the tool and the machined surface is:

In the formula, f _l ⁽⁰⁾ (z,x(z)), f _r ⁽⁰⁾ (z,x(z)) are the initial cutting edge equations of the left and right edges of the tool respectively, a _p is the theoretical cutting depth of the tool, Cl _l , Cl _r are the contact lengths of the left and right flanks of the tool respectively, Z _k is the distance between the centerline of the kth thread tooth counted from the feed direction and the x-axis of the machine tool coordinate system, ε _rl and ε _rr are the tool left , Right-edge tool tip angle, B ₀ is the thread height.

Furthermore, the formulas of the transient contact length and contact width between the flank of the tool and the machined surface of the workpiece in the second step are:

(1) The formula for the transient contact length between the flank of the tool and the machined surface of the workpiece is:

(2) The formula for the transient contact width between the flank of the tool and the machined surface of the workpiece is:

Cw ^(Q) = a ₁ ·v _c (t)+a ₂ ·[f(t)+S _z (t)+Δz ₁ +Δz ₂ ]+a ₃ +[S _y (t)+Δy ₂ ]· cosα

In the formula, a _p (t) is the cutting depth of the tool instantaneously, S _x (t), S _y (t), S _z (t) are the vibration displacements of the tool in the x, y, and z directions respectively, and κ _r is the main force of the tool Deflection angle, v _c (t) is the main movement speed of the tool, f (t) is the feed per tooth, △ z ₁ is the axial rotation error of the machine tool holder, △ y ₂ and △ z ₂ are the y and z directions of the tool The installation error of , a ₁ , a ₂ , a ₃ are the x, y, z displacements of the tool assembly respectively, and α is the back angle of the tool.

Furthermore, in the sixth step, the left and right edge symmetrical forming turning tools are used, and the left and right thread surfaces of the threaded specimens are dry-turned with equal margin under the same process parameters. The tools used in the experiment can be Spring-type turning tool with changing tool head, the material is high-speed steel (W18Cr4V), the cutting edge of the tool is a left-right symmetrical structure, connected by the top edge and the left and right cutting edges, and the rake angle of the left and right edges is 0° , the blade inclination angle is 0°, the left and right blade nose angles are 105°, 105°36' respectively, the left and right cutting edge angles are 75°, 105°36' respectively, and the left and right blade relief angles are They are 7°10' and 5°28' respectively, the angle between the left and right blades is 30°36', and the arc radius of the tool tip is 52mm and 44mm respectively.

The beneficial effects of the present invention are: the present invention proposes a calculation and test method for the difference in cutting behavior of the tool interface between the left and right cutting edges of the large-pitch trapezoidal external thread tool. According to the cutting motion and cutting posture of the tool during the cutting process, Identify the characteristic parameters and influencing factors of the contact behavior of the knife-work interface, analyze the hierarchical structure of the knife-work contact relationship, and analyze the important influencing factors. Based on the parameter extraction, the calculation model of the knife-work contact length and the knife-work contact width is established; The force model of the tool during the cutting of the left and right edges of the pitch thread reveals that there are obvious differences in the stress states of the left and right edges; according to the model revealing the difference in shear deformation during cutting, the deformation coefficients during the cutting process are respectively constructed and the composition relationship of relative slip; according to the analysis of mechanical behavior and shear deformation behavior, it reveals the composition and difference of shear angle and friction angle when cutting with left and right blades; Under the same process parameters, the equal margin dry turning experiment was carried out on the left and right thread surfaces of the thread specimen. The results showed that the chip shape, the flank wear width of the left and right blade tools and the left and right , There are obvious differences in the vibration signals when the right edge is cutting.

Description of drawings

Figure 1 is a diagram of the contact relationship between the left and right cutting edges of the tool and the machining transition surface;

Figure 2 is a diagram of the contact relationship between the front and flank surfaces of the tool and the workpiece;

Figure 3 is a hierarchical structure diagram of the characteristic parameters and influencing factors of the contact relationship between tool workers;

Figure 4 is a schematic diagram of the contact between the flank of the tool and the machined surface of the workpiece during the initial cutting;

Figure 5 is a schematic diagram of the contact between the flank of the tool and the machined surface of the workpiece after cutting a certain stroke;

Fig. 6 is a diagram of the tool contact relationship under the influence of factors such as machine tool and tool vibration, installation error, displacement and deformation;

Fig. 7 is a schematic diagram of the force on the left-edge cutting large-pitch thread;

Fig. 8 is a schematic diagram of the force on the right edge cutting large-pitch thread;

Fig. 9 is a schematic diagram of shearing deformation of left edge cutting chips;

Fig. 10 is a schematic diagram of shear deformation of right-edge cutting chips;

Fig. 11 is a theoretical chip formation model diagram of large-pitch external thread turning by the left edge of the tool;

Fig. 12 is a diagram showing the relationship between force and angle when the left edge is turning large-pitch thread turning;

Fig. 13 is a diagram of the relationship between force and angle when turning large pitch threads with the right edge;

Figure 14 is the chip of the last cut when the left edge of the tool is cutting, the measurement area and the shape of the chip;

Figure 15 is the chip of the last cut when the right edge of the tool is cutting, the measurement area and the shape of the chip;

Figure 16 is a comparison diagram of the stress field of the old and new process machine tools;

Figure 17 is a comparison of the wear width of the left and right flanks of the tool under the same cutting stroke (a in the figure is a comparison of the wear width of the left and right flanks of the tool with a cutting stroke of 26.13m; The comparison chart of the wear width change of the left and right flank of the tool; c is the comparison chart of the wear width change of the left and right flank of the tool with a cutting stroke of 182.91m; d is the wear width of the left and right flank of a tool with a cutting stroke of 261.30m Change comparison chart);

Fig. 18 is a scheme diagram of setting the external thread sensor when turning large-pitch external thread;

Fig. 19 is a vibration signal diagram of a left-blade turning large-pitch thread tool (a in the figure is a time-domain vibration signal diagram of a left-blade turning large-pitch thread tool; b is a frequency-domain vibration signal of a left-blade turning large-pitch thread tool);

Fig. 20 is a vibration signal diagram of a right-blade turning large-pitch thread tool (a in the figure is a time-domain vibration signal diagram of a right-blade turning large-pitch thread tool; b is a frequency-domain vibration signal of a right-blade turning large-pitch thread tool);

detailed description

Implementation example 1: Hierarchical structure and characteristic variables of tool-worker contact relationship in turning large-pitch thread

(1) When the left and right edges of the large pitch thread are cut, because the working angle of the tool is different from the marked angle, the total cutting force and cutting stroke of the left and right edges of the tool are different, which will lead to inconsistent machining results of the left and right edges . During the initial cutting, the motion parameter variables of the left and right cutting edges of the tool are shown in Table 1.

Table 1 The basic variables of the relationship between the cutting motion of the left and right blades of the tool

In the table, n _l is the cutting speed of the left blade, n _r is the cutting speed of the right blade, v _cl is the main motion speed of the left blade, v _cr is the main motion speed of the right blade, v _fl is the feed speed of the left blade, and v _fr is the speed of the right blade Edge feed speed, e _l is the normal vector of the machined surface when the left edge is cutting, and e _r is the normal vector of the machined surface when the right edge is cutting; is the helix angle of the specimen.

The solution equations for each motion variable in Table 1 are:

In the formula, d is the major diameter of the large-pitch thread, n is the spindle speed, and P is the pitch of the large-pitch thread.

During the initial cutting, the geometric parameter variables of the left and right cutting edges of the tool are shown in Table 2.

Table 2 The basic variables of the geometric relationship between the left and right cutting edges of the tool

In the table, Y means that the left and right blades are consistent, and N means that the left and right blades are not consistent; the different relationships between the variables in Table 2 when cutting the left and right blades are:

κ _rl + ε _rl = πκ _rr = ε _rr (2)

In the formula, d ₁ is the small diameter of the large pitch thread.

During the cutting process, different working angles of the tool will change the stress and deformation of the tool during the cutting process. The actual working angles during the cutting process of the left and right edges of the tool are shown in Table 3.

Table 3 Tool Angle and Posture during Left and Right Edge Cutting

It can be seen from Table 3 that if the cutting tool adopts a symmetrical forming turning tool, the actual working rake angle when cutting with the left edge is larger than that for cutting with the right edge, and the actual relief angle is smaller than that for cutting with the right edge. Therefore, when cutting with the left edge, The deformation of the cutting layer and the chip friction resistance on the rake face are small, the cutting temperature is low, and the main cutting force on the tool is small when the left edge is cutting.

From the above analysis, it can be seen that when the left and right blades of the tool are turning large-pitch threads, the left and right blades use the same cutting motion, but due to the existence of the helix angle, the attitudes of the left and right blades of the tool are different. Therefore, when cutting with the left and right blades regardless of the working angle, if the tool adopts a symmetrical forming turning tool and the same cutting parameters are used in the cutting process, that is, when the same process is used, the cutting performance of the left and right blades can be guaranteed. layer area is the same. Due to the different working angles of the tool when the left and right edges are cutting, the total cutting force and cutting stroke of the left and right edges of the tool are different, which will lead to inconsistent machining results of the left and right edges.

(2) The contact relationship between the large pitch thread cutting tool and the tool includes: the contact between the rake face and the chip, the contact between the cutting edge and the machining transition surface of the workpiece, and the contact relationship between the flank and the machined surface of the workpiece. According to the actual cutting method and processing status of the large-pitch thread, the contact relationship between the left and right cutting edges of the tool and the machining transition surface and the contact relationship between the front and flank surfaces of the tool and the workpiece can be obtained when the large-pitch thread is cut in layers in the axial direction. As shown in Figure 1 and Figure 2.

In the figure, _n is the rotational speed of the _workpiece , v _c and v _f are the main motion speed and feed speed of the selected reference point of the tool respectively; d ₁ , d ₂ , and d represent the small diameter, middle diameter, and large diameter of the thread respectively, z _k represents the distance between the centerline of the kth tooth counted from the feed direction and the x-axis of the machine tool coordinate system, and Cl _l and Cw _l are respectively The average contact length and contact width between the left flank of the tool and the workpiece, Cl _r , Cw _r are the average contact length and width between the right flank of the tool and the workpiece, l _cl , l _cr are the left and right rake faces of the tool, respectively The length of contact with the chip, l _el and l _er are the actual cutting lengths of the left and right cutting edges of the tool respectively, A _γl and A _αl are the rake face and flank face of the tool when the left edge is cutting, A _γr , A _αr are the rake face and flank face when the right edge of the tool is cutting, respectively, is the helix angle of the large-pitch thread, γ _0l and γ _0r are the rake angles marked on the left and right edges of the tool respectively, α _0l and α _0r are the rear angles marked on the left and right edges of the tool respectively, α _0le and α _0re are the actual tool angles respectively Left and right edge relief angles, ε _rl and ε _rr are the tool tip angles of the left and right edges of the tool respectively, κ _rl and κ _rr are the cutting angles of the left and right edges of the tool respectively, r _εl and r _εr are the cutting angles of the tool respectively The arc radius of the left and right blades, ρ _l is the radius of the left cutting edge, and ρ _r is the radius of the right cutting edge.

From Fig. 1, Fig. 2 and the analysis, it can be concluded that when the large-pitch thread is cut in layers in the axial direction, the external influencing factors of the contact relationship between the tool and the workpiece during the large-pitch thread machining are shown in Table 4.

Table 4 Influencing factors of knife-worker contact relationship

In the table, S _x , S _y , S _z are the displacements of the tool under vibration, c _j is the tool installation error, Δx _p , Δy _p and Δx _d , Δy _d are the displacements of the tool assembly, R ^(Q) _u is the curvature of the tool flank contour unit, S ^(Q) is the actual contact area between the tool flank and the machined surface of the workpiece, Δx ₁ and Δz ₁ are the spindle rotation errors in the x and z directions, respectively, L', d _z are the axial and radial tool deformation respectively.

The characteristic parameters and influencing factors of the contact relationship between the cutting edge and the front and flank surfaces and the workpiece are shown in Tables 5 to 7.

Table 5 The contact characteristic parameters between the tool cutting edge and the machining transition surface

Table 6 Contact characteristic parameters between tool rake face and chips

In the table, φ _l and φ _r are the shearing angles when the left and right edges of the tool are cutting, respectively.

Table 7 The contact characteristic parameters between the flank of the tool and the machined surface of the workpiece

In Table 7, Cw _l ^(Q) and Cw _r ^(Q) are respectively the contact width between the flank and the machined surface of the workpiece when the left and right cutting edges of the tool change with the cutting stroke, S _l ^(Q) , S _r ^{( Q)} is the instantaneous contact area between the flank and the machined surface of the workpiece when the cutting of the left and right edges of the tool changes with the cutting stroke; C _hl ^(Q) and C _hr ^(Q) are respectively When the stroke changes, the instantaneous contact depth between the flank and the machined surface of the workpiece, R ^(Q) _u is the curvature of the contour unit of the tool flank.

In the initial stage of cutting, only a small part of the cutting edge and the flank of the tool are in contact with the workpiece, which can be approximated as a line contact; Under the influence of the wear state measured by the experimental tool, it can be deduced that the contact relationship between the tool and the workpiece has changed, resulting in wear on the flank of the tool. At this time, the contact type between the tool and the workpiece is the surface contact of the flank .

From the above analysis, it can be concluded that the hierarchical structure relationship of the characteristic parameters and influencing factors of the knife-worker contact relationship is shown in Figure 3.

It can be seen from Figure 3 that the above hierarchical structure relationship will cause dynamic changes in the contact relationship between the left and right blades, and the difference in the structure and wear of the left and right blades of the tool makes the contact relationship between the left and right blades exist. At the same time, it can be seen that the contact length l c between the rake face and the chip, the contact length l _e between the cutting edge and the transition surface _, the contact length Cl and the contact width Cw between the flank and the machined surface of the workpiece are important parameters to determine the contact relationship between tool and tool.

Implementation Example 2: Calculation method of the left and right knife contact length and knife contact width

Since the cutting edge and flank of the tool are severely worn during the process of cutting large-pitch threads, the tool-tool contact relationship can be characterized by the attitude of the cutting edge and the state of the flank during each period of cutting.

According to the initial state of the cutting edge of the tool, take the tool tip as the origin, and follow the right-handed Cartesian coordinate system to establish a rectangular coordinate system composed of x, y, and z axes, where the x direction is the direction of the radial feed speed of the tool, The y direction is the cutting speed direction, and the z direction is the tool axial feed direction. The curve equations F _l ⁽⁰⁾ (Z, X) and F _r ⁽⁰⁾ (Z, X) of the left and right edges of the tool in the tool coordinate system can be obtained by Matlab curve fitting, and the coordinate transformation is applied to convert the tool coordinate system is the equation of the machine tool coordinate system, f _l ⁽⁰⁾ (z, x) and f _r ⁽⁰⁾ (z, x). Let the starting point and the ending point of the cutting edge participating in the cutting part be E ₁ and F ₁ respectively, and the coordinate values in the machine tool coordinate system are:

Therefore, taking the left flank as an example, the initial cutting edge equation f _l ⁽⁰⁾ (z, x) is known, and the initial contact length between the left flank of the tool and the machined surface can be expressed as follows:

Similarly, when cutting with the right edge, the initial contact length between the right flank of the tool and the machined surface can be expressed as follows:

In the formula, a _p is the theoretical cutting depth of the tool, z _k is the distance between the center line of the kth thread tooth counted from the feed direction and the x-axis of the machine tool coordinate system, ε _rl and ε _rr are the corner angles of the left and right edges of the tool, respectively , B ₀ is the thread height.

In theory, the initial contact relationship between the tool and the workpiece should be line contact, that is, the initial width and depth should be both 0, and the included angle between the flank and the processed surface of the workpiece is In actual situations, due to the precision error of the machine tool itself and the installation error of the tool, there is a certain contact area between the tool flank and the workpiece. Suppose the axial rotation error of the machine tool holder is △z ₁ , and the installation error of the tool is △x ₂ , △y ₂ , △z ₂ , then suppose the contact width between the flank of the tool and the machined surface of the workpiece is as follows:

Cw ⁽⁰⁾ = Δz ₁ ·tan(α-φ) (6)

In the formula, α is the tool relief angle, is the thread helix angle.

Initially, since the edge arc radii of the left and right edges of the tool are close to 0, the contact area of the tool flank is close to 0, that is, the contact type between the tool and the workpiece is line contact. The type of relationship is difficult to maintain. After cutting for a period of time, the contact relationship between the tool and the workpiece will become a stable surface contact and will continue. The contact relationship at this time is used as the initial contact relationship of the tool.

Taking the origin of the tool coordinate system as the center, along the b direction, rotate the tool coordinate system O-XYZ counterclockwise around the X axis by α ₁ degree, and record the newly obtained coordinate system as O ₁ -X ₁ Y ₁ Z ₁ . In this coordinate system, the tool contact relationship between the tool flank and the workpiece during the cutting process is shown, as shown in Figure 4 and Figure 5.

In Figure 4 and Figure 5, curve 1 represents the cutting edge equation at each moment of the cutting edge, which gradually changes with the cutting process, and can represent the change process of the tool cutting edge and workpiece contact posture; curves 2, 3, and 4 are Indicates the boundary curve of the contact between the tool flank and the workpiece, in which the position of curve 2 changes with the change of the tool relief angle, but the shape remains unchanged; curve 3 is affected by vibration, tool deformation and displacement, and curve 4 It is determined by the workpiece and is mainly affected by the radial depth of cut.

In the cutting process, due to the influence of factors such as machine tool and tool vibration, installation error, displacement and deformation, the characteristic parameters of the contact relationship between the tool and the workpiece are mainly the contact width with the main movement speed v _c , the feed rate f, the machine tool tool The axial rotation error of the frame, the installation error of the tool and the vibration amplitude and other factors change, as shown in Figure 6.

Assume that the theoretical cutting depth of the tool is a _p , the instantaneous cutting depth of the tool is a _p (t), the feed rate of each tool is f _i , and the vibration displacement generated by the tool vibration during the cutting process is respectively S _x (t), S _y ( t), S _z (t), the axial rotation error of the tool holder of the machine tool is △z ₁ , and the installation error of the tool is △x ₂ , △y ₂ , △z ₂ , therefore, the flank of the tool and the machined surface of the workpiece The transient contact length and contact width are shown in formula (7) and formula (8).

Cw ^(Q) = a ₁ ·v _c (t)+a ₂ ·[f(t)+S _z (t)+Δz ₁ +Δz ₂ ]+a ₃ +[S _y (t)+Δy ₂ ]· cosα (8)

In the formula, κ _r is the cutting edge angle of the tool, v _c (t) is the main movement speed of the tool, f(t) is the feed rate per tooth, a ₁ , a ₂ , and a ₃ are the tool components x, y, and z respectively Amount of displacement.

The contact length l _e between the rake face of the tool and the chip refers to the length of contact between the chip and the rake face when the chip starts to flow out and breaks away from the tool during the process of turning large-pitch threads with the left and right edges. The calculation formula is as follows (9).

In the formula, a _c is the cutting thickness, Λ _h is the deformation coefficient, and φ is the shear angle.

Therefore, it can be seen from the above analysis that when the left and right edges of the tool are turning large-pitch threads, the contact relationship between the tool and the tool changes dynamically with the change of the cutting stroke. The contact relationship between the tool and the tool under various influencing factors is shown in Figure 6.

Implementation example 3: force model of left and right edge cutting tools

When the left and right edges of the tool cut large-pitch threads, there are two sources of cutting force: one is the resistance produced by the elastic deformation and plastic deformation of the metal in the cutting layer, chips and the metal on the surface of the workpiece; Frictional resistance between surfaces. When using a forming turning tool to turn a large pitch thread, the force state of the tool is different when the left edge is turned and the right edge is turned. The specific force state is shown in Figure 7 and Figure 8.

In the figure, F _γl and F _γr are the friction force acting on the rake face of the left and right cutting edge respectively, F αl and F _αr are the friction resistance acting on the _{flank face of the left and right cutting edge respectively, F γNl ,} F _αNl is the normal force acting on the front and flank surfaces of the left cutting edge respectively; F _γNr and F _αNr are the normal forces acting on the front and flank surfaces of the right cutting edge respectively; F _{γl and γNl} are the normal forces acting on the left cutting edge The resultant force of edge F _γl and F _γNl , F _{γr, γNr} is the resultant force of right cutting edge F _γr and F _γNr , F αl _{, αNl} is the resultant force of left cutting edge F _{αl and F αNl ,} F _{αr, αNr} is the resultant force of right cutting edge F The resultant force of _αr and F _αNr , F _fl , F _fr are the feed forces acting on the left and right edges respectively, F _l , F _r are the total cutting forces acting on the left and right edges respectively, F _cl , F _cr are respectively is the main cutting force acting on the left and right edges; v _f is the axial feed rate of the tool, v _cl and v _cr are the main movement speeds of the tool when cutting the left and right edges respectively, _vel and v _er are respectively The resultant movement speed of the tool when the right edge is cutting; _{β l} , β _r are the friction _angles on the left and right edge _cutting respectively _; Mark the rake angle and rear angle of the right blade, γ _0le and α _0le are the working rake angle and working relief angle of the left blade respectively, γ _0re and α _0re are the working rake angle and working relief angle of the right blade respectively.

Among them, when cutting with the left edge:

When cutting with the right edge:

It can be seen from Fig. 7 and Fig. 8 that the resultant cutting force F _l and F _r are in the main section of the tool, and the resultant cutting force and main cutting force of the tool when the left and right edges are cutting can be obtained from the force analysis of chips, as shown in formula (14) ~ Formula (17) shown.

The resultant cutting force when the left edge is cutting is:

The main cutting force F _cl is:

In the formula, τ is the shear stress, h _Dl is the cutting thickness when the left edge is cutting, b _Dl is the cutting width when the left edge is cutting, φ _l is the shear angle when the left edge is cutting, is the helix angle.

The resultant cutting force when the right edge is cutting is:

The main cutting force F _cr is:

In the formula, h _Dr is the cutting thickness when the right edge is cutting, b _Dr is the cutting width when the right edge is cutting, and φ _r is the shear angle when cutting the right edge.

From the above analysis, when it is assumed that the rake angles of the left and right blades of the tool are the same and the cutting parameters are the same, due to the existence of the helix angle, the working rake angle of the tool when the left edge is cutting is larger than that of the right edge, and the cutting force of the left and right edges There is a significant difference between the main cutting force composition and the main cutting force; at the same time, the cutting force on the tool is closely related to the shear angle and friction angle when the left and right blades are cutting, and then the shear deformation behavior of the tool in the cutting process restricts the left and right blades. , The cutting force of the right blade affects the force difference between the left and right blades.

Implementation example 4: Calculation method of deformation coefficient and relative slip of the left and right cutting edges of the tool

In the process of large-pitch thread turning, taking left-edge cutting as an example, assuming that the cutting edge is absolutely sharp, that is, the flank surface does not contact the workpiece, the shear deformation of the chip when turning large-pitch external thread left and right edge cutting is established. And the chip formation model when the left edge is cutting, as shown in Fig. 9, Fig. 10 and Fig. 11.

In the figure, h _chl and h _chr are the chip thickness when the left and right edges are cutting respectively, F _δhn is the normal pressure on the shearing surface, F _δh is the shearing force on the shearing surface, F _γn is the force on the rake face Normal force F _γ , F _γ is the friction force on the rake face, and γ ₀ is the rake angle of the tool.

When cutting with the left edge of the tool:

When cutting with the right edge:

In the formula, Λ _hl and Λ _hr are the deformation coefficients of chips during left and right edge cutting, respectively, and ε _l and ε _r are the relative slippage during left and right edge cutting, respectively.

From the above analysis, it can be seen that in the cutting process, when the tool adopts a symmetrical forming turning tool, the influencing factors of the deformation coefficient when the left and right blades are cutting are shear angle, rake angle and helix angle, but when the left and right blades are cutting The composition of the deformation coefficient is inconsistent. Due to the influence of the helix angle, there is a difference in the deformation coefficient of the chip when the left and right blades are cutting. This is because the existence of the helix angle changes the contact relationship between the left and right blades. , which leads to differences in the deformation coefficients when the left and right blades are cutting, and the shear deformation is different when the left and right blades are cutting. Helix angle and deformation coefficient, and because the helix angle has different effects on the working rake angle of the tool when the left and right edges of the tool are cutting, that is, when the tool is cutting with the left and right edges, the mechanism of relative slip is different, and then the left and right edges There are obvious differences in the relative slippage of the tool during cutting.

Implementation Example 5: Calculation method of shear angle and friction angle of the left and right blades of the tool

In the process of large-pitch thread turning, the forces acting on the chips are: the friction force and the normal force of the friction force on the rake face, the shear force and the normal force of the shear force on the shear surface, and the relationship between the two pairs of forces The resultant forces balance each other. Since the working angle of the tool is different when the left and right blades turn large-pitch threads, the relationship between chip force and angle is different when the left and right blades turn large-pitch threads, as shown in Figure 12 and Figure 13.

In the figure, F _cl ^w , F _cr ^w are the main cutting forces on the chips when the left and right edges are cutting, F _fl ^w , F _fr ^w are the feed resistances on the chips when the left and right edges are cutting, F _γl ^w , F _γr ^w are the friction force of the rake face of the tool acting on the chips when the left and right edges are cutting, F _γNl , F _γNr are the friction forces of the rake face of the tool acting on the chips when the left and right edges are cutting respectively F _l ^w , F _r ^w are the chip formation force when the left and right blades are cutting, F _δhl , F _δhr are the shear forces on the shear plane when the left and right blades are cutting, F _δhN1 , F _δhN2 are the normal forces on the shear plane when the left and right edges are cutting, respectively.

When cutting with the left edge of the tool:

From Figure 12, the shear angle can be obtained as:

The average friction coefficient and friction angle of the tool-chip interface can be calculated by the main cutting force _Fc and the feed force _Ff , namely:

When cutting with the right edge:

From Figure 13, the shear angle can be obtained as:

The friction angle is:

The shear angle and friction angle change in different forms when the left and right blades of the tool are cutting, but the influencing factors are the same; because the shear angle φ and the friction angle β have the following relationship:

When cutting with the left edge, the relationship between the shear angle and the friction angle of the rake face is:

When cutting with the right edge, the relationship between the shear angle and the friction angle of the rake face is:

Therefore, when the left and right edges of the tool are cutting, the shear angle increases with the increase of the rake angle, that is, when the rake angle increases, the chip deformation decreases. Therefore, increasing the rake angle under the condition of ensuring the strength of the cutting edge is beneficial to improve the cutting process; at the same time, the shear angle decreases with the increase of the friction angle, that is, when the friction angle increases, the chip deformation increases, so careful grinding The rake and flank of the tool or the use of cutting fluid can also improve the cutting process.

From the above analysis, it can be seen that when the left and right edges of the tool are cutting, the influencing factors of the shear angle and the friction angle are the same, but the composition of the shear angle and the friction angle is different, that is, when the left and right edges are cutting, the shear angle and the friction angle are different. The mechanism of formation is different. It can be seen from formula (32) and formula (33) that the deformation coefficients of the left and right blades must be different. The chip shape is inconsistent, and the friction behavior between the chip and the rake face of the tool is different, which will lead to obvious differences in the wear pattern of the tool when cutting with the left and right edges.

Implementation example 6: Experimental test method for the difference in cutting behavior between the left and right blades of the tool

(1) In order to effectively verify the behavior difference of the tool when the left and right blades are turning large-pitch threads in layers, the experiment uses a symmetrical forming turning tool with left and right blades. The thread surface is dry-turned with equal allowance.

The material of the test piece is 35CrMo quenched and tempered, the structure is a right-handed trapezoidal external thread, the number of heads is 1, the thread length is 190mm, the major diameter is 148mm, the minor diameter is 132mm, the middle diameter is 140mm, the thread pitch is 16mm, and the tooth half angle is 15° .

The tool used in the experiment is a spring-type turning tool with a replaceable head, and the material is high-speed steel (W18Cr4V). The cutting edge of the tool has a left-right symmetrical structure. The rake angle of the blade is 0°, the inclination angle of the blade is 0°, the corner angles of the left and right blades are 105°, 105°36' respectively, and the leading angles of the left and right blades are 75°, 105°36' respectively. , The left and right blade relief angles are 7°10' and 5°28' respectively, the left and right blade angles are 30°36', and the radius of the knife tip arc is 52mm and 44mm respectively.

The experimental speed is 10rpm, the axial single machining allowance is 0.05mm, the cutting stroke of the left and right blades is 26.13mm, 104.52mm, 182.91mm and 261.30mm respectively, and the tool stops to measure the tool wear. A total of 4 measurements are made, and the measurement is completed. Afterwards, the original tool is used to continue cutting, and the total removal allowance in the left and right axial directions is 2.5mm. In the experiment, the vibration signals of each tool during the cutting process were extracted at the same time.

The experimental machine tool for turning large-pitch thread adopts CA6140 traditional lathe, the experimental instrument is VHX-1000 super depth-of-field microscope, and DH5922 transient signal test and analysis system.

(2) Collect the chips from the last cut of the left and right edges in the experiment respectively, and use the VHX-1000 super depth-of-field microscope to measure the chip shape in the designated area. The measurement area and chip shape are shown in Figure 14 and Figure 15.

It can be seen from the chip shape when the left and right edges of the tool are cutting the same tool in Figure 14 and Figure 15 that there is a significant difference in the degree of deformation of the workpiece when the left and right edges are cutting. In the same area, the chip surface when the right edge is cutting is smoother than that when the left edge is cutting, the degree of deformation along the cutting thickness direction is relatively small, and the number of convex and concave places on the surface is small; The degree of bending is more severe than that obtained when cutting with the left edge. As can be seen from the figure, the degree of deformation and the state of the same measurement position vary greatly.

(3) In order to reveal the difference in tool wear during left and right edge cutting, the tool flank wear width was taken as the measurement target, and the VHX-1000 ultra-depth-of-field microscope was used to measure the tool flank wear width under different cutting strokes. The method is shown in Figure 16.

In the figure, O is the tool tip, X is the distance between the wear position and the tool tip along the length direction of the cutting edge (mm), Z is the tool flank wear width (μm), S is the length of the cutting edge involved in cutting (μm), and Z _y1 ~ Z _yk is the tool flank wear width (μm) at k measurement points when the cutting stroke is Y.

Using the above measurement method, the measurement results of four left and right flank wear experiments are shown in Table 8 and Table 9. Among them, the distances X ₁ , X ₂ , ..., X ₁₀ from the tool tip along the length direction of the cutting edge are respectively 0.95mm, 1.9mm, 2.85mm, 3.8mm, 4.75mm, 5.7mm, 6.65mm, 7.6mm, 8.55mm, 9.5mm.

Table 8 Data table of left flank wear width

Table 9 Right flank wear width data table

Under the same cutting stroke, the change of the wear width of the left and right flanks of the tool is shown in Figure 17.

It can be seen from the figure that under the same cutting stroke, the wear width of the left flank of the tool is generally larger than that of the right flank of the tool, and the change degree is more severe than that of the right flank; with the increase of the cutting stroke, the wear width of the left and right flanks of the tool The wear degree tends to be stable, and at the same time, the wear width of the left and right flanks never exceeds the rated maximum wear width during the cutting process.

(4) When turning large-pitch external threads, the sensor is set at the end of the spindle, and the sensors are respectively set on the machine tool spindle along the cutting speed direction and the feed speed direction; at the same time, in order to prevent the sensor from interfering with the tool cutting, the sensors are set separately Below and to the left of the tool closest to the tip, as shown in Figure 18.

According to the above experimental method, the time domain and frequency domain vibration signals of the tool during the last cut of the left and right blade turning large-pitch threads are tested, and the measurement results are shown in Figure 19 and Figure 20.

From the above figure, the tool vibration characteristic parameter values under left and right edge cutting conditions can be obtained, as shown in Table 10.

Table 10 Tool vibration characteristics under left and right edge cutting conditions

In the table, K is the kurtosis, a ₀ is the root mean square value of the initial vibration, a _rms is the effective value of the vibration, m is the number of main vibration frequencies, f ₁ is the first main frequency, f ₂ is the second main frequency, f ₃ is the third main frequency, f ₄ is the fourth main frequency, E _p1 , E _p2 , E _p3 , and E _p4 are spectrum values respectively. Among them, the kurtosis K reflects the impact existing in the tool cutting. The larger the kurtosis value, the greater the external excitation mutation in the system, the greater the energy change, and the greater the impact effect. Therefore, the kurtosis K can be used to identify and evaluate The sudden change of external excitation and the impact intensity when the tool cuts in and out. a ₀ and a _rms represent the effective value of the vibration acceleration of the system in a certain period of time before cutting and cutting process respectively, and the strength of vibration signals in different periods can be identified by using this parameter.

From the time-domain signal analysis of the tool in Figure 19 and Figure 20, it can be seen that when the tool is cutting with the right edge, the impact of the tool in the x, y, and z directions is stronger than that of the left edge, and the z direction is the strongest, followed by the y direction. The x direction is the weakest, indicating that the impact of the direction of feed movement and cutting speed during external thread machining has a great influence on the machining process; from the frequency domain signal analysis of the figure, it can be seen that the main frequency of vibration is the same when cutting with the left edge and cutting with the right edge , when the left edge is cutting, the first dominant frequency is higher than that of the right edge, which means that the periodic motion of the left edge is more frequent than that of the right edge. The tool is mainly affected by the vibration of the machine tool in the x direction, and the high frequency vibration caused by the cutting force in the y and z directions big.

The difference between the present invention and the disclosed technology: the existing research on the contact relationship between the tool and the workpiece is mainly aimed at the typical motion form of the tool and the workpiece in the cutting process, analyzing the geometry and motion characteristics of the tool contact during the machining process, using the trilinear difference method Calculate the distance from the sampling point on the tool surface to the workpiece during the movement, and determine the points in the contact area according to the distance value, from which the relevant parameters of the tool contact can be obtained, which provides a high-efficiency and high-precision tool contact calculation in cutting processing Methods. However, this method does not consider the changes in chip shape and tool wear during machining, and cannot fully reveal the cutting behavior of the tool interface.

The present invention proposes a method for calculating and testing the difference in cutting behavior between the left and right cutting edges. According to the cutting motion and cutting posture of the tool during the cutting process, the characteristic parameters and influencing factors of the contact behavior of the tool interface are identified, and the tool tool interface is established. Calculation model of contact length and tool contact width; establishment of force model of tool when turning left and right edges of large-pitch external thread; construction of compositional relationship between deformation coefficient and relative slip during cutting; analysis based on mechanical behavior and shear deformation behavior , to reveal the composition and difference of the shear angle and friction angle when the left and right blades are cutting; propose an experimental test method for the difference in the cutting behavior of the left and right blades of the tool, and obtain the tool turning during the formation of the left and right thread surfaces The chip shape, the flank wear state of the left and right blade tools and the vibration signal of the tool verify the correctness of the mechanical analysis and shear deformation of the left and right blade turning large pitch threads.

Claims (4)

1. calculating and the method for testing of the knife work interface cutting behavior otherness of left and right cutting edge, it is characterised in that including following Step：

The first step, determine turning steep-pitch thread knife work contact relation hierarchical structure and characteristic variable；

According to the Tool in Cutting motion in working angles and cutting posture, the characteristic parameter and shadow of knife work interracial contact behavior are recognized The factor of sound, analyzes knife work contact relation and carries out hierarchical structure and characteristic variable；

Second step, left and right angle of throat work contact length and knife work contact width, which are calculated, to be analyzed；

3rd step, set up left and right sword cutting tool stress model；

4th step, deformation coefficient and Relative sliding computational methods using the left and right cutting edge of cutter, disclose the left and right sword of cutter Cutting deformation otherness；

5th step, the angle of shear and angle of friction computational methods using the left and right cutting edge of cutter, disclose the left and right sword of cutter rubbed Otherness in journey；

6th step, using the left and right cutting edge cutting behavior otherness experimental test procedures of cutter, cut when disclosing left and right sword cutting Bits form, left and right sharpening undermine the otherness in left and right sword dynamic cutting behavior；

To use the symmetrical formation type lathe tool of left and right sword, the left and right flank of screw thread test specimen is carried out under identical technological parameter Etc. surplus Dry Turning, the Chip Morphology in designated area is measured for the super depth-of-field microscopes of VHX-1000 by laboratory apparatus and led to Cross DH5922 transient signal detecting and analysing systems test out cutter time domain when left and right knife car cuts last knife of steep-pitch thread and Frequency domain vibration signal, analyzes the left and right sword cutting behavior otherness test result of cutter.

2. calculating and the method for testing of the knife work interface cutting behavior otherness of left and right cutting edge according to claim 1, It is characterized in that：The initial contact length formula of knife face and machined surface is after cutter in second step：

(1) the initial contact length formula of the left back knife face of cutter and machined surface is：

(2) the initial contact length formula of knife face and machined surface is after cutter is right：

In formula, f_l ⁽⁰⁾(z,x(z))、f_r ⁽⁰⁾(z, x (z)) is respectively the left and right sword initial cuts sword equation of cutter, a_pIt is theoretical for cutter Cutting depth, Cl_l、Cl_rThe respectively left and right rear knife face contact length of cutter, Z_kFor from several k-th of the ridge of direction of feed Line and the distance of lathe coordinate system x-axis, ε_rl、ε_rrThe respectively left and right angle of throat wedge angle of cutter, B₀For height of thread.

3. calculating and the method for testing of the knife work interface cutting behavior otherness of left and right cutting edge according to claim 1, It is characterized in that：Knife face is with workpiece machined surface transient state contact length and contact width formula after cutter in second step：

(1) knife face is with workpiece machined surface transient state contact length formula after cutter：

(2) knife face is with workpiece machined surface transient state contact width formula after cutter：

Cw^(Q)=a₁·v_c(t)+a₂·[f(t)+S_z(t)+Δz₁+Δz₂]+a₃+[S_y(t)+Δy₂]·cosα

In formula, a_p(t) it is cutter transient state cutting depth, S_x(t)、S_y(t)、S_z(t) be respectively cutter x, y, z to vibration displacement, κ_rFor cutter tool cutting edge angle, v_c(t) it is cutter main motion speed, f (t) is feed engagement, △ z₁For lathe cutter saddle, axially revolution is missed Difference, △ y₂、△z₂For cutter y, z to alignment error, a₁、a₂、a₃Respectively toolbox x, y, z is to displacement, and α is after cutter Angle.

4. calculating and the method for testing of the knife work interface cutting behavior otherness of left and right cutting edge according to claim 1, It is characterized in that：It is to use the symmetrical formation type lathe tool of left and right sword in 6th step, to screw thread test specimen under identical technological parameter The surplus Dry Turnings such as left and right flank progress, it is interchangeable cutter head spring lathe tool to test used cutter, and material is at a high speed Steel (W18Cr4V), tool in cutting sword is left and right symmetrical structure, is connected by top sword with left and right two cutting edges, before left and right sword Angle is 0 °, and cutting edge inclination is 0 °, and left and right angle of throat wedge angle is respectively 105 °, 105 ° of 36', left and right sword tool cutting edge angle difference during cutting For 75 °, 105 ° of 36', left and right edge clearance angle is respectively 7 ° of 10', 5 ° of 28', and left and right sword angle is 30 ° of 36', corner radius point Wei not 52mm, 44mm.